Hi,
While this is an excellent explanation of comb filtering, I would suggest that for most listeners using common source material--movie soundtracks and multi-channel music playback--and not with pink-noise test signals, comb filtering does not produce significant audible effects of any consequence.
After all, John, comb filtering is always taking place even listening in 2-channel stereo. Every time you move your head an inch or centimeter, there are comb filtering effects--altnernate reinforcement and cancellation of frequencies.
For those who are interested in learning how to hear comb filtering with pink noise, set your playback system to 2-channel stereo, play a pink-noise signal, sit exactly in the sweet spot and gradually shift your head to the left and to the right while facing the front soundstage.
Listen to the higher frequency portion of the pink-noise signal and you'll hear the hi-frequency content vary slightly as the high frequencies are reinforced and cancelled. That's comb filtering, and it's always taking place.
As far as expecting guests to hear what you are hearing, that will never be the case for any guest sitting off-axis whether you use a single center channel speaker or dual centers. Certainly using dual centers above and below the screen is a practical and effective solution for large screen projection when a single center results in the dialog located away from the screen. The latter, in my view, is far more distracting than any theoretical problems of comb filtering with program material.
Regards,
